Penetrating finishes

Penetrating finishes such as stains and water-repellent preservatives ( 7,8) leave little or no continuous coating on wood surface. Because there is no coating, there is no failure by blistering or peeling. These finishes are ideally suited for rough-textured surfaces difficult to paint effectively. 

The oil-base, semi-transparent, penetrating finishes are generally comprised of a resin, a solvent, a UV-absorbing pigment, a wax, and a preservative (7). 

Two basic types of finishes (or treatments) are used to protect wood surfaces during outdoor weathering those that form a film, layer, or coating on the wood surface, and those that penetrate the wood surface to leave no distinct layer or coating. Film-forming materials include paints of all description, varnishes, lacquers, and also overlays bonded to the wood surface. Penetrating finishes include preservatives, water repellents, pigmented semitransparent stains, and chemical treatments. 

Penetrating. The penetrating finishes are the second broad classification of natural wood finishes. These finishes do not form a film on the wood surface. 

Waterborne Salts. Waterborne inorganic salts are a special group of penetrating finishes. These surface treatments result in a finish similar to the semitransparent penetrating finishes because they change the color of the wood and leave a surface deposit of material similar to the pigment found in the semitransparent stains. 

DuofoL [Hart Chem. Ltd.] Sulfated ester wetting agent, dispersant, penetrant, finishing agent for textiles. 

Penetrating Finishes. Penetrating finishes, which do not form a film over the wood, include oils, water repellents, stains, preservatives, and surface treatments. 

Penetrating finishes such as stains and water-repellent preservatives leave little or no continuous coating on wood... 

Penetrating finish n. A low-viscosity oil or varnish which penetrates wood, leaving a very thin film at the surface. 

Penetrating Finish A finish that sinks into the substrate, as opposed to settling on the surface. 

Handbook of chemistry and physics, 52nd edn. Weast RC (ed). The Chemical Rubber, Boca Raton, FL) Penetrating Finish n A low-viscosity oil or varnish which penetrates wood, leaving a very thin film at the surface. 

The primary adhesive used ia hardwood plywood is urea—formaldehyde (UF) mixed with wheat flour as an extender to improve spreadabiUty, reduce penetration, and provide dry-out resistance. A catalyst may also be added to UF resias to speed the cure or to cause the UF to cure. Scavengers also may be added to reduce formaldehyde emissions from finished panels. If more water-resistance is requited using a UF bond, small amounts of melamine maybe added, producing a melamine—urea—formaldehyde (MUF) adhesive. 

Phosphonomethylated Ethers. A phosphoms-containing ether of ceUulose can be prepared by the reaction of cotton ceUulose with chioromethylphosphonic acid [2565-58-4] ia the presence of sodium hydroxide [1310-73-2] by the pad-dry-cure technique (62). Phosphoms contents of between 0.2 and 4.0% are obtained. This finish is durable but has high ion-exchange properties and is flame resistant only as the ammonium salt. DurabUity on medium weight fabrics is obtained with chi oromethylph osph onic diamide. This finish has never penetrated the flame retardant market (63). 

Leather finishes penetrate to a greater or lesser extent and have a profound effect on the grain or wrinkle characteristics of the leather. Penetration of the resia into the leather tightens the grain but may produce a surface stiffness and a tendency toward grain cracking upon flexing. The development of leather finish resins and the appHcation of these finishes is done by specialty houses. 

Such a unique hierarchical stmcture gives leather several advantages (/) transformabiUty into any desired shape, (2) resistance to penetration of wind, water, and other materials, (3) breathabiUty (water vapor and air permeabiUty, and water absorption), (4) flexibiUty, and (5) processibiUty into finished forms having a grain or suede surface. 

Evaporation Retardants. Small molecule solvents that make up the most effective paint removers also have high vapor pressure and evaporate easily, sometimes before the remover has time to penetrate the finish. Low vapor pressure cosolvents are added to help reduce evaporation. The best approach has been to add a low melting point paraffin wax (mp = 46-57° C) to the paint remover formulation. When evaporation occurs the solvent is chilled and the wax is shocked-out forming a film on the surface of the remover that acts as a barrier to evaporation (5,6). The addition of certain esters enhances the effectiveness of the wax film. It is important not to break the wax film with excessive bmshing or scraping until the remover has penetrated and lifted the finish from the substrate. Likewise, it is important that the remover be used at warm temperatures, since at cool temperatures the wax film may not form, or if it does it will be brittle and fracture. Rapid evaporation occurs when the wax film is absent or broken. 

Methylene chloiide formulas are the most common organic chemical removers. The low molar volume of methylene chloride allows it to rapidly penetrate the finish by entering the microvoids of the finish. When the solvent teaches the substrate, the remover releases the adhesive bond between the finish and the substrate and causes the finish to swell. The result is a bhstering effect and an efficient rapid lifting action. Larger molecule solvents generally cannot... 

The knitted fabric is subjected to a finishing operation in which a suitable backing material is appHed to penetrate the yam contact points and stabilize the stmcture. This process is usually accompanied by a heat treatment which stabilizes the fabric and conditions the pile. 

Water Repellency and Water Resistance. Water repeUency is defined as the abihty of a textile fiber, yam, or fabric to resist wetting, whereas water resistance is a general term appHed to a fabric s abiUty to resist wetting and penetration by water (2). A third term, waterproof, is appHed to those fabrics that do not allow any water penetration at all. Waterproof fabrics are generally coated with an impermeable surface layer that does not allow air permeabihty. Water-repellent finishes are hydrophobic compounds that are appHed to fabrics to inhibit water penetration while still allowing air permeabihty. 

Rotary atomisation produces an excellent surface finish. The spray has low velocity, which allows the electrostatic forces attracting the paint particles to the ground workpiece to dominate, and results in transfer efficiencies of 85—99%. The pattern is very large and partially controlled and dkected by shaping ak jets. The spray when using a metallic cup has relatively poor penetration into recessed areas. Excessive material deposited on the edges of the workpiece can also be a problem. 

The reservoir interior should be smooth to avoid poekets and provide an unbroken finish for any interior proteetion. Reservoir wall-to-top junetions may be welded from the outside by utilizing full-penetration welds. 

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